The present invention relates to a variable image-display that displays variable images comprised of visible pixels.
A sign having a static image comprising a retroreflective sheet is disclosed in, for example, U.S. Pat. No. 5,050,327. The image of this sign is formed from a light-transmitting prismatic retroreflective sheet. The prismatic retroreflective sheet comprises a prismatic sheet having prism elements that are called cube comer prisms that can reflect light in a specific direction by the effective use of a refraction function and a total reflection function of the prism elements. In addition, the prismatic sheet is made of a light-transmissive polymeric material, and thus the sheet as a whole allows light to transmit therethrough. Accordingly, the retroreflective sheet effectively reflects the illumination light entering the surface of the prismatic sheet, and allows the sign image to be brightly observed by an observer. On the other hand, the light entering the back surface of the prismatic sheet can transmit through the sheet and thus the prismatic sheet allows the sign image to be brightly observed by an observer.
In addition to reflective sheets that increase the visibility in a relatively narrow observation angle range, wide observation angle type reflective sheets that increase the visibility in a wide observation angle range are used. As a sign-illuminating system that uses a sign having an image comprising a wide observation angle type reflective sheet, Japanese Patent No. 2,910,868 (corresponding to U.S. Pat. No. 5,818,640) discloses an external illumination type sign-illuminating system comprising a sign and an external light source. In this system, the light source is arranged so that it emits light that enters the sign surface at an incident angle in the range between 0 degree and 30 degrees. In general, a retroreflective sheet having a sign image thereon is adhered to the sign surface. The reflective sheet, that is improved to have a wide observation angle range, comprises optical refractive elements such as glass beads, prism elements, etc., and reflection elements such as deposited metal films, etc. In the case of the above described cube comer prism elements, the light can be reflected in a specific direction using the total reflection function of the prisms without reflection elements.
Furthermore, signs are known, that can display variable images comprised of a plurality of light-emitting pixels. Such image-displays commonly have the following components:
(A) a substrate having a front surface which is observed by an observer, and a back surface opposing said front surface, and
(B) a plurality of pixel elements that are arranged on the front surface of the substrate in rows and columns, (i.e. perpendicular to the row directions).
Each pixel element has an internal light source as an essential component. Well known examples of such variable image-displays include electronic signs, and the like. An electronic sign-type image-display is disclosed in, for example, WO97/39436. The variable image-display uses pixel elements comprising light-emitting panels that have one or more light-emitting elements such as an LED as the internal light sources.
In the case of such a variable image-display an observable image is created by a plurality of light-emitting pixels. The background that functions to contrast the image, clear, are composed of comprises pixels that do not emit light. The image can be varied by controlling the light emission from the pixels with the aid of a computer so that pixels at certain positions on the front surface of the substrate are allowed to emit light while other pixels are not.
However, the above-described variable image-displays may not display images, if a part or all of the light-emitting elements cannot emit light because of failure of the light-emitting elements or electronic control circuits.
Therefore, it has been proposed to include the above-described reflective members comprising prismatic sheets (prismatic sheet reflectors) in parts corresponding to the light-emitting panels. The variable image-display is improved so that an image can be observed by reflecting light from an external light source at a high luminance with the reflectors on the surfaces of the light-emitting parts, even if the light-emitting elements do not emit light.
In the case of such a type of a variable image-display a light-transmitting reflector comprising a prismatic sheet is provided on the surface of the light-emitting parts, and thus the light from the light-emitting elements illuminates the light-emitting part from its backside. The light illuminated from the backside of the prismatic sheet passes through the prismatic sheet, and allows the image to be brightly observed by the observer. Accordingly, this type of variable image-display can function in the same way as the above-described electronic sign-type variable image-display when the internal light sources thereof (e.g. light-emitting elements) emit light.
Such a variable image-display has a structure shown in FIG. 6. In the variable image-display (9), each pixel element comprises
(i) a fixed part having a light-emitting part (93) formed on the front face of the substrate (90), an adjacent area (94) that is adjacent to the light-emitting part, and a border line (96) formed between the light-emitting part and the adjacent area, and
(ii) an opaque shutter (91) that is rotatably fixed to a respective axis in parallel with the border line (96), and is movable between a first static state to shield light-emitting part(s) (93), and a second static state to expose the light-emitting part(s) (93), the shutter having a second face (912) facing an observer in a first static state and a first face (911) facing the. observer in a second static state.
In the second static state, the light-emitting part (93) and the first face (911) of the shutter are observed while being arranged parallel with each other on the front face of the substrate form a visible pixel. In this state, the light-emitting part emits light. In general, prismatic sheet reflectors having the same color are arranged on the light-emitting part (93) and the first face (911) of the shutter.
In the first static state, the light emitting-part (93) is shielded. Thus, the light-emitting part (93) and the first face (911) of the shutter cannot be observed, even when they are externally illuminated. The second face (912) of the shutter and the adjacent area (94) that faces the observer in the first static state, are generally colored black. Thus, they can effectively form the non-light-emitting pixel as a background, that functions to contrast the image formed with the visible (i.e. light emitting) pixels. Accordingly, the image can be varied by controlling the states of the pixels so that some pixel elements (shutters) are in the second state and the corresponding light-emitting parts (93) are allowed to emit light, while the rest of the pixel elements are in the first state. The static states of the pixel elements are determined independently of each other.
In general, the light-emitting part (93) consists of (1) an opening (e.g. hole) provided in the substrate and a prismatic sheet reflector provided to cover the entire opening, or (2) a light-emitting-reflection module which is detachably provided in an opening provided in the substrate.
A variable image-display having the light-emitting parts of structure (1) is disclosed in, for example, U.S. Pat. No. 5,050,327; while one having the light-emitting parts of structure (2) is disclosed in, for example, U.S. Pat. Nos. 5,148,156, 5,500,652 and 5,790,088. The light-emitting-reflection structure (2) comprises a small-sized light-emitting device such as an LED, and a prismatic sheet reflector. Thus, in the case of failure of the light-emitting device, the module of each light-emitting part is replaced. To facilitate the exchange of the module, the light-emitting-reflection modules are detachably mounted in the respective openings. In the case of structure (1), at least one internal light source (e.g. a fluorescent lamp, etc.) is provided on the backside of the substrate to illuminate the back surfaces of the prismatic sheet reflectors through the openings. In either structure, a plurality of openings are required to form the plurality of light-emitting parts.
The conventional variable image-displays having shutters are advantageous for the production of signs displaying simple words or sentences, but are not suitable for the production of image-display or devices to display variable signs that can change from one static image to another static image. Such variable-displays or devices are being used in place of conventional road signs or directional signs carrying printed static images. The reason for this will be explained with reference to FIG. 6.
In the case of the conventional signs carrying printed static images, the backgrounds are typically a relatively bright color (e.g. red, yellow, blue, green, etc.). However, in the conventional variable image-display, the adjacent areas (94) and the second faces (912) of the shutters (91) are colored black. If they were colored a bright color, the difference of brightness between the non-light-emitting pixels and the light-emitting pixels would be too large. This would result in the sign having a different appearance in comparison with conventional printed static signs.
It is advantageous for images comprised of a plurality of visible pixels to be substantially continuously seen, to display relatively complicated designs or marks or characters (e.g. having a relatively large number of strokes such as Chinese characters) and to be similar in appearance to conventional printed static image signs. To this end, the size (width) of the frame (95) between the adjacent openings should be made as small as possible so that the image can be seen continuously. However, the reduction of the width of the frame (95) will decrease the mechanical strength of the frame (95) itself, and in turn, the mechanical strength of the substrate (90) having a plurality of such frames (i.e. with a narrow width). To increase the mechanical strength of the substrate, the thickness of the substrate may be increased, or a material having a larger density is used to produce the substrate. However, the increase of the thickness of the substrate, or the use of the material having a larger density make it difficult to decrease the thickness of the display or to reduce the weight of the display.
For example, some road signs have image-display planes with a relatively large area (e.g. 1 m2 or larger). To maintain the compatibility (i.e. in size) with such a large static image sign, a variable image-display having an image-displaying plane with a relatively large area would be produced. The conventional variable image-display includes the weight of the light-emitting units, the light source(s), and the space in which the light-emitting units are mounted, making it difficult to reduce the weight and thickness of the display as a whole while maintaining the size of the display area.
The present invention discloses a variable image-display, that can form a variable image sign similar to a conventional signs carrying a printed static image. The variable-image display advantageously has a similar apperance to a conventional printed static image, is amenable to a reduced weight or reduced thickness display as a whole, and allows the image comprising a plurality of visible pixels to be seen continuously.
With the variable image-display of the present invention, the images can be illuminated with an external light source and observed. Thus, it is not necessary for the variable image-display to have a light source that allows the pixels to emit light. The pixels can be observed brightly (at a high luminance) with an external light source, since the pixels have reflective surfaces. Accordingly, the variable image-display of the present invention can be suitably used as a sign such as a road sign and a directional sign, or a component of such a sign.
The present invention relates to an improvement of a variable image-display in which each pixel element comprises (a) two fixed faces on the front surface of a substrate, and (b) an opaque shutter, which is rotatable between two static states, wherein, in one static state, the shutter shields one of the fixed faces so that it becomes unobservable allowing the other fixed face to be exposed so that it is observable. Either the fixed face surface or the back surface of the shutter is observable in each static state. In such image-display, the pixel elements are changed between two static states, and form visible pixels in each static state. Thus, the image comprised of such visible pixels can be changed to display a plurality of images.
In one aspect, the present invention provides a variable image-display comprising an opaque substrate having a front surface that is observable, and a back surface opposing said front surface, and a plurality of pixel elements that are arranged on said front surface of the substrate in rows and columns (i.e. that are perpendicular to the row directions). Each pixel element comprises a fixed part having a first face that is fixed to said front surface of the substrate, and a second fixed face adjacent to said first fixed surface, and a border line between said first fixed face and said second fixed face, and an opaque shutter having a first and second observable face which is rotatable around an axis and parallel with said border line between said fixed faces. In a first static state, said second fixed face of the fixed part and said second observable face of the shutter are juxtaposed each other to form a first visible pixel. In a second static state, said first fixed surface of the fixed part and said first observable face of the shutter are juxtaposed each other to form a second visible pixel. The static states of each pixel element can be determined independently of each other or synchronously with each other. Thereby an image comprised of a plurality of the visible pixels is displayed. The first and second fixed faces consist of a reflective surface of a substantially opaque reflective member that covers said front surface of the substrate and the first and second observable faces consist of a reflective surface of a substantially opaque reflective member that covers the surface and back surface of said shutter. The image may be illuminated with an external light source (e.g. car headlight) when observed.
In the variable image-display of the present invention, the two fixed faces (the first and second fixed faces) on the front surface of the substrate, and the surface and back surface (the first and second observable faces) of the shutter consist of respective reflective surfaces of substantially opaque reflective members. The image comprised of such visible pixels is illuminated with an external light source, and can be observed at a high luminance. Accordingly, it is not necessary to form openings (through holes) in the substrate and utilize the transmitted light from the backside of the substrate in order to increase the visibility of the visible pixels. Thus, the above problem is solved, and the sign carrying the variable sign that is similar in appearance to a conventional sign carrying a printed static image can be obtained.
The reflective member used in the present disclosure is usually a reflective sheet such as a retroreflective sheet. Thus, the reflective surface can be easily formed by the adhesion of the reflective sheet to the component such as the substrate.